Telephone-exchange system.



W. R. BROUGH AND W. L. DODGE. TELEPHONE EXCHANGE SYSTEM.

APPLlCATlON FILED APR. 22. 1 18.

1,326,475. Patented Dec. 30,1919.

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57m ie/ewse //4 van 70/8 MOW/0m R. Brag/9h. W/Mam L Dodge W. R. BROUGH AND W. L. DODGE.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED APR. 22, I918.

Patenfed Dec. 30, 1919.

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UNITED STATES PATENT OFFICE.

WILLIAM R. BROUGH, OF EAST ORAN GE, AND WILLIAM L. DODGE, O.'E MAPLEWGOD, NEW 3' ERSEY, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Dec. 30, 1919.

' Application filed April 22, 1918. Serial No. 230,189.

To all whom it may concern:

Be it known that we, VVILLIAM and VILLIAM L. DODGE, citizens of the United States, residing at East Orange, in the county of Essex, State of New Jersey, and at Maplewood, in the county of Essex, State of New Jersey, respectively, have invented certain new and useful Improvements in Telephone-Exchange Systems, of

which the following is a full, clear, concise,

and exact'description. I

This invention relates to telephone exchange systems. and more particularly to such systems in which trunk circuits are employed for completing connections betweentelephone lines terminating at different central oflices or switchboards.

The object of this invention is to provide improved signaling means for systems of this character.

In accordance with a feature of this invention two relays provided at the incoming end of a trunk circuit operate in response to alternating current transmitted over the trunk circuit upon the connection of a link circuit with the outgoing end to cause the operation of a signaling ,device at theincoming end which now serves as a guard signal, and upon the subsequent disconnection of the link circuit from the outgoing end of the trunk circuit alternating current of a different strength is transmitted over the trunk circuit to operate one of the two relays for again causing'the operation of the signaling device which now serves as a disconnect signal.

In accordance with another feature of this invention, other relays provided in the trunk circuit respond upon connection being established between the trunk circuit and the called-for line to connect a source of alternating current to the trunk circuit for causing the operation of a signaling device in the vconnected link circuitwhich serves as a R. Bsooen rnow'control the connection of a source of alternating current with the called-for line for operating the usual call bell at the station thereon.

This invention will be more fully understood from the following description taken in connection with the accompanying drawings, wherein Figures 1 and 2 whenplaced end to end with Fig. 2 at the right of Fig. 1 illustrates one embodiment of this invention.

As shown in the drawings, a trunk circuit A extends from one central office to a second central oflice. A cord circuit B located at the first central office may form part of the connection between a calling toll line D and the outgoing end of the trunk circuit A. The incoming end of the trunk circuit A may connect with the outgoing end of a toll switching trunk circuit C which extends from a second central office to another switchboard which may be located in the second central office or in a third central office, The incoming end of the toll switching trunk C may connect directly with a local telephone line B. All apparatus shown in Fig. 1 is-located at a first central office or switchboard X; that shown to the left of the dotted line 33 of Fig. 2 is located at the second switchboard Y; and that shown. to the right of dotted line 33, at the third switchboard Z.

The two sides ofthe trunk circuit A between the first and second switchboards 'may besimplexed for the transmission of telegraph messages between the two operators. This scheme of communication between operators may be employed for transmitting the proper instructions regarding the setting up of the connection between subscribers.

The operator at the first switchboard X having been advised that connection is desired between the toll line D and the line of subscriber E which terminates at, the local switchboard Z, connection with which must be established through the switchboard Y, may communicate by telegraph over the simplex circuit with the operator at the switchboard Y. The telegraph sets, which are shown at M and N, may consist of the usual Morse telegraph key, sounder and control relays. The operator at the first switchboard X ascertaining that connection with the line of subscriber E is to be completed by way of trunk circuit A inserts calling plug 5 of the cord circuit B into jack 6 of the trunk, circuit A; Relays 7, 4 and 8 thereupon operate over a circuit from battery through the left-hand winding of relay 7, winding of relay 4, S1eeVe contacts ofthe plug 5 and the jack 6 and the winding of relay 8 to ground. Relay 7 in operating completes parallel circuits through lamp 9 and relay 10 and relay 11. Relay 11 is of the fast-operate and slow-release type, while relay 10 is of the slow-operate type. Relay 11 therefore operates before relay 10 and in so doing opens the energizing circuit of the relay 10 and the lamp 9. The lamp 9 and the Delay 10 will, therefore, not operate upon the closure of the contact of relay 7. Relay .8, in operating, causes the operation of slowrelease relays l2 and 13 and slow-operate relay 14, the circuits therefore being as follows: Relay 12: from battery through the Winding of relay 12, contact 15 of relay 14 and left-hand alternate contact of relay 8 to ground. Relay 13: from battery through the winding of relay 13, normal contact" ofslow-release relay 16 and the left-hand alternate contact of relay 8 to ground. Relay 14: from battery through the winding of relay 14, contact of ringing response relay 17, normal contact of ringing response relay 18 and the left-hand alternate contact of relay 8, to ground. Relay 14:, in operating, opens the energizing circuit of relay 12 which is thereby denergized. Upon the operation of relay 13, a sourceof current 19 is connected with the trunk circuit over a circuit from the source of current 19 through the right-handalternate contact of relay 8,

the lower alternate contact of relay 13, a

winding of repeating coil 20, condenser 21,

' anoth'er winding of repeating coil 20 and the upper alternate contact of relay 13 to ground. 1 Current traversing these two windings of the repeating coil 20 induces current into the other two' windings which thereupon flows over the two conductors of the trunk circuit to the second switchboard Y for a purpose to be described presently. Relay 13, in operating, causes the energization of a slow-operate relay 25 over a circuit from battery through the winding of relay 25, middle alternate contact of relay 13 and the left-hand alternate contact of relay 8 to ground. Relay 25, in operating, establishes a locking circuit for itself through its left-hand contact and the lefthand alternate contact of relay 8 to ground the slow-operate relay 25 cooperate to provide for the connection of the source of ourrent 19 with the trunk circuit for a predetermined length of time. In this manner, an impulse of definiteduration is connected with the trunk circuit-upon the operation of ,current from the source 19 when transmitted over the trunk circuit through retardation coil 30. Relay 28, in operating, removes a short circuit from relay 31, which thereupon operates upon the closure of the alternate contact of relay 27 over a circuit from battery through the alternate contact of relay 27, resistance 32 and the winding of relay 31 to ground. Relay'31, in operating, causes the energization of a slow-release relay 33,

which upon being energized is locked up over a circuit from battery through the normal contact 34 of relay 35, lower alternate contact and lower winding of relay 33 to ground.' Resistance 58 prevents the operation of slow-release relay 80 upon the energization of relay 31. Upon the energization of relay 33 lamp 36 is lighted over a cir- 'cuit from battery through the lamp 36, lower nprmal. contact of relay 37 and the upper alternate contact of relay 33 to ground: Since the currentfor operating relays. 27 and 28 is connected with .the trunk circuit A only while the relay 13 is energized, these relays 27 and-28 release their armatures, thereby causing the release of relay 31. Upon the release of relay 27, a slow-release relay 38 operates over a cir- CHltfIOlTl battery through the normal contact of relay 27, winding of relay'38 and upper alternate contact of relay 33 to ground. Relay 38, in operating, causes the energization of'relay 35 over a circuit from battery through the alternate contact of relay 38, lower normal'contact and winding of relay 35 and the upper alternate contact of relay 33 to ground. Relay 35 upon being energized establishes a locking circuit for itself from battery through contact 39 and winding of relay 35 and the upper alternate contact of relay 33 to ground. Relay 35 upon being energized also transfers the looking circuit of relay 33 from battery through contact 34 of relay 35 to battery through the alternate contact of relay 38 and contact 57 of relay 35, thereby maintaining relay 33 operated and lamp 36 lighted.

The operator at the switchboard Y observing the lighted condition of the lamp 36 is thereby advised that the originating operator has connected with the proper trunk circuit. The operator at switchboard Y may thereupon insert plug of the trunk circuit A into jack 41 of the toll switching trunk circuit C. Relay 42 thereupon operates over a circuit from battery through the winding of relay 42, sleeve contacts of the plug 40 and the jack 41 and resistance 44 to ground. Relay 42, in operating, causes the operation of relay 37 which extinguishes the lamp 36 and closes a normally open contact in the tip strand of the trunk circuit A Relay 45, in the toll switching trunk circuit C, thereupon operates over a circuit from battery through the left-hand winding of relay 45, left-hand normal contact of relay 46, a winding of repeating coil 47, tip contacts of the jack 41 and the plug 40, upper alternate contact of relay 37, upper normal contact of relay 48, retardation coil 49, contact 50 of relay 35, winding of relay 51, retardation coil 52, lower normal contact of relay 48, ring contacts of the plug 40 and the jack 41, another winding of repeating coil 47, right-hand normal contact of relay 46 and the right-hand winding of relay 45 to ground. Relay 45, in operating, causes the operation of relay 46 and the lighting of lamp 553 over a circuit from battery through the lamp 53, lower normal contact of relay 54, right-hand winding of relay 46 and the alternate contact of relay 45 to ground. Re lay 46, in operating, first establishes, a holding circuit through the left-hand winding of relay 45 and the alternate contact of relay 46, and then opens the original energizing circuit of relay 45, thereby to prevent the operation of supervisory relay 51 of the trunk circuit A.

The toll switching operator at the switchboard Z upon observing the lighted condition of the lamp 53 knows that the connection has been built up as far as the toll switching trunk circuit C, and having been previously advised as to the number of the desired line, inserts plug 60 of the toll switching trunk G into jack 61 of line E.- Relay 54 and cutoff relay 55 thereupon operate, the operation of thevformer extinguishing the lamp 53'and causing the deenergization of relay 46 which in releasing its armature re'elstablishes the original energizing circuit of relay 45 in which supervisory relay 51 is included. The supervisory relay 51 1s thereby energized. Cutofi' relay55, in operating, disconnects the line relay 56 from the line.

Supervisory relay 51 upon being energized causes the operation of relay 62 over a circuit from battery through the normal contact of relay 27, contact of supervisory relay.

51 and the winding of relay 62 to. ground. Relay 62, in operating, causes the energization of relay 63 over a circuit from battery through the contact of relay 62, winding of relay 63 and resistance 64 to ground. Re

' \Vhen relay 63 is energized, the upper and lower normal contacts thereof which are in the talking conductors of the trunk circuit are opened and a source of alternating current 67 is connected through the lower alternate contact of relay 63 with the righthand .windings of the repeating coil 26. Current is thereupon induced into the lefthand windings of the repeating coil 26, and through the inductive action of the windings of the repeating coil 20, current is in turn induced into a circuit including the left-hand windings of the repeating coil 20, thereby to cause the operation of the ringing response relay 17. Relay 17, in operating, opens the energizing circuit of .relay 14 which thereupon releases its armatures. Upon the closure of contact 15 thereof, slow-release relay 12 is energized to open its contact which is in the ring conductor of the trunk circuit A. The closure of contacts 68, 69 and 72 of relay 14 connectsbattery through the windings of retardation coil 7 O with the talking strands of the trunk circuit A. Supervisory relay 71 is thereupon operated over a circuit from battery through theleft-hand winding of retardation coil 70,- cont'acts 68 and 72 of relay 14, ring contacts of the jack 6 and the plug 5, lower normal contact of ringing key 73, retardation coil 75, winding of supervisory relay 71, retardation coiI'Z 6, upper normal contact of ringing key 73;, contact of relay 4, tip contacts of the plug 5 and the jack 6, contact 69 ofrelay 14 These two relays 63 and 65 cuit of slow-operate relay 14. The length of time of the deenergization of relay '63 is so short, however, that theslow-operate relay 14 does not have time to open its normal and close its alternate contacts. Therefore, supervisory relay 71 will remain energized and the lamp 77 lighted while relays 63 and 65 are operating.

The originating operator at the switchboard X, observing the lighted condition of the supervisory lamp 7 7 knows that the connection has been completely set up to the line of subscriber E and that the lighting of the lamp is a signal that everything is in proper condition for signaling subscriber E. The originating operator may thereupon sig nal subscriber E by actuating ringing key 73 to connect a source of alternating current 78 with the trunk circuit A. Ringing response relay 18 thereupon operates over a circuit from the source of ringing current 78, the lower alternate contact of ringing key 73, ring contacts of the plug 5 and the jack 6, contact 72 of relay 14, condenser 79, winding of relay 18, contact 69 of relay 14, tip contacts of the jack 6 and the plug-5 and the upper alternate contact of ringing key 73 to ground. The actuation of ringing key 73 opens the circuit of supervisory relay 71,

causing its denergization and the e ace-' ment of the lamp 77. Relay 18, in operating, causes the energization of the slow-release relay 13 over a circuit from battery through the winding of relay 13, alternate contact of relay 18 and the left-hand alternate contact of relay 8 to ground. Relay 13 upon being energized connects the source of alternating current 19 with the trunk circuit A for causing the operation of relays 27 and 28 upon the first subsequent release of relay 63. Relay 13, in operating, opens the circuit of ringing response relay 17 which is thereupon deenergized, but does not cause the energization of relay 14 for ringing response relay 18 is now operated. Immediately upon the energization of relay 27 relay 62 is deenergized to stop the operation of the vibrating relays 63 and 65, thereby disconnecting the source of alternating current 67 from the end of trunk circuit A extending to switchboard X. Relay 27 in operating, also opens the circuit of and releases sloW-release relay 38 and causes the operation of relay 31. Relay 31 operates before relay 38 releases and establishes an alternate locking circuit for relay 33 through the right-hand contact of relay 31. Relay 31, in operating, also causes the energization of a slow-release relay 80 over a circuit from battery through contact 81 of relay 35, winding of relay 80 and left-hand contact of relay 31 to ground. Relay 80, upon closing its right-hand contact, establishes another locking circuit for relay 33, the purpose of which will more fully hereinafter appear.

Upon the release of relay 38, relay 48 op erates over a circuit from battery through the normal contact of relay 38, winding of relay48 and left-hand contact of relay 80 to ground. Relay 48 upon being energized first opens the tip and ring conductors of the trunk circuit A, thereby releasing supervisory relay 51. fRelay 48 on being energized also connects a source of alternating current 82 to the plug end of the trunk circuit A, thereby causing the operation of ringing response relay 83 of the toll switching trunk C over a circuit from the source of alternating current 82 through the lower alternate contact of relay 48, ring contacts of the plug 40 and the jack41, winding of relay 83, condenser 84, tip contacts of the jack 41 and the plug 40, the upper alternate contact of relay 37 and the upper alternate contact of relay 48 to ground. Relay 83, in operating, causes the operation of relay 46 and a ringing relay 85 over a circuit from battery through the left-hand winding of relay 46, winding of ringing relay 85 and the contact of relay 83 to ground. Relay 46, in operating, closes its alternate contact, thereby maintaining relay 45 energized, while the original energizing circuit thereof is open at the normal'contacts of relay 46 and the upper and lower normal contacts of relay 48. The operation of ringing relay 85 connects a source of ringing current 86 with a line of subscriber E for causing the operation of the usual call bell. Upon the restoration of the ringing key 73 in normal condition, relays 18, 13, 27, 28, 31 and 80 release, relays 14 and 38 ope-rate and relays 48, 83, 85 and 46 release. Relay 80 is made slow-release so that relay 33 will be maintained energized until relay 38 closes its alternate contact. If the subscriber E has not ,at this time removed the receiver from the switchhook, supervisoryrelay 51 energizes, causing the operation of relay 62 which sets in operation the relays 63 and 65 for intermittently connecting the source of current 67 with that end of the trunk circuit extending to switchboard X for again causing the energization of supervisory relay 71 which lights the supervisory lamp 77 as a ringing signal. This lamp will remain lighted until the operator at switchboard X again actuates the ringing key 73 or until contact of relay 87, right-hand winding of relay 46 and the alternate contact of relay 45 to ground. Relay 46, in operating, first establishes at this alternate contact a circuit for maintaining relay 45 operated and then opens at its normal contacts, the original energizing circuit of relay 45. Supervisory relay 51, which is in the energizing circuit of relay 45, now releases, whereupon relays 62, 63, 65 and 17 release, relay 14 operates, relays 12 and 71 release and the supervisory lamp 77 is extinguished. The

talking circuit from the calling subscriber D to called subscriber E is now completed and conversation may take place.

At the conclusion;of the conversation, the subscribers restore the receivers to the switchhoolzs. The 'restoration of the receiver to the switchhook by the calling subscriber D and the operation of the generator thereat cause the energization of relay 90 which releases relay 11 Relay 1O thereupon operates over a circuit from battery through the contact of relay 7, the winding of rela 10 and the lamp in parallel, contact of relay 11 and the normally closed contact of listening key 91 to ground. Relay 10, in operating, establishes a locking circuit for itself through its own contact so that this relay 10 remains energized and the lamp 9 remains lighted when the contact of relay 11 is opened upon the energization thereof due to the subsequent release of relay 90. The lighting of the lamp 9 serves as a disconnect signal from the calling subscriber.

The restoration of the receiver to the switchhook by subscriber E releases supervisory relay 87, whereupon relay 46 releases to again include the energizing circuit of relay 15, the supervisory relay 51. Relay 51 now operates, closing the energizing circuit of the slow-release relay 62. Relay 62, in operating, causes the successive energization and deenergization of relays 63 and which intermittently connect the source of alternating current 67 to that end of the trunk circuit extending to switchboard X.

As already described in detail, relay 1T responds to the connection of alternating current to the trunk circuit and in opening its contact releases relay 14, whereupon relay 71 is operated" to light the supervisory lamp 77. Lamps 9 and 77 being lighted at the same time serve as disconnect signals to theoriginating operator who may now disconnect the cord circuit B from the calling subscribers line and withdraw the plug 5 from the jack 6. Upon the removal of the plug 5 from the j ac1 ;6, relay 8 releases, causing the energization of relay 13 over a circuit from battery through the winding of. relay 13, alternate contact of slow-release relay 16 and the normal contact of relay 8 to ground. The disconnection of the cord circuit B from the calling line D and the trunk circuit A restores to'normal position all apparatus of the cordcircuit. Relay 8 now being released, thee'nergization of relay 13 connects a source of alternating current 19 to the trunk circuit through impedance coil 30, and marginal relay 28 at the switchboard Y does not respond but the relay 27' does. The release of relay. 8 causes the deenergiz'ation' of slow-operate relay 25 and slow-release relay 16 and then slow-release relay 13, which disconnects alternating current from source 19 from the trunk circuit A.

Inasmuch as relay 28 does not respond, the

short circuit about the winding of relay 31 is not removed, hence relay 31 does not oper-- ate When relay 27 is energized and relay 28 denergized. The energization of relay 27 causes the release of relay 38, thereby opening the locking circuit of relay-'33. Since neither relay 31 nor 80 is operated at this time, relay 33 is totally deenergized and re: leases its armatures, thereby causing the lighting of the lamp 36 over a circuit from battery through the lamp 36, lower alternate' contact of relay 37 and the normal contact of relay 33 to ground. The lighting of this lamp 36 at this time serves as a disconnect signal to the operator at switchboard Y who may now withdraw the plug 40 from the jack 11, whereupon all apparatus of the trunk circuit A is restored to normal condition.

The withdrawal of the plug 40 from the jack 41 causes the deenergization of relay 45, thereby causing the lighting of the lamp 53 over'a circuit from battery through the lamp 53, lower alternate contact of relay 54, resistance 92 and the normal contactof relay 45 to ground. The lighting of the lamp 53 serves as a disconnect signal to the toll switching operator at switchboard Z, who may now withdraw the plug 60 from the jack 61, whereupon all apparatus of the toll switching trunk circuit C and the telephone line E is restored to normal condition.

What is claimed is:

1. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current, means in the trunk circuit respon sive to the connection of the link circuit -with the trunk circuit for connecting therewith the source of'alternating current and responsive to the disconnection of the link circuit from the trunl; circuit to again connect therewith the source of alternating current, an extension circuit at the second switchboard, a signaling device thereat, and means responsive to the first connection of the course of alternating current with the trunk circuit to operate the signaling device and responsive to the second connection of the source of alternating current to the trunk circuit while connected with the extension circuit for again operating the signaling device.

2. A telephone exchange system comprising a trunk circuit'extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current, means in the trunk circuit responsive to the connection of the link circuit with the trunk circuit for connecting therewith the source of alternating current and responsive to the disconnection-of the link circuit from the trunk circuit to again connect therewith the source of alternating current, an extension circuit at the second switchboard, a signaling device thereat, and a relay at the second switchboard energized upon the first connection of the source of alternating current with the trunk circuit for operating the signaling device and deenergized upon the second connection of the source of alternating current with the trunk circuit while connected with the extension circuit for again operating the signaling device.

3. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current, means in the trunk circuit responsive to theconnection of the link circuit with the trunk circuit for connecting therewith the source of alternating current and responsive to the disconnection of the link circuit from the trunk circuit to again connect therewith the source of alternating current, an extension circuit at the second switchboard, a signaling device thereat, a ringing response relay responsive to both the first and second connections of the source of alternating current with the trunk circuit, a second ringing response relay at the second switchboard responsive to the first connec tion of the source of alternating current with the trunk circuit, and a relay energized upon the response of both ringing response relays for operating the signaling device and deenergized upon the response of the first rin ing response relay only while the trunk circiiit is connected with the extension circuit for again operating the signaling device.

4. A telephone. exchange system comprising a trunk circuit extending from a first to'a second switchboard, a link circuit at the first switchboard, a source of alternating current, means in the trunk circuit responsive to the connection of the link circuit with the trunk circuit for connecting therewith the source of alternating current and responsive to the disconnection of the link circuit from the trunk circuit to again connect therewith the source of alternating current, an extension circuit at the second switchboard, a signaling device thereat, a ringing response relay at the second switchboard responsive to both the first and second connection of the source of alternating current with the trunk circuit, a second ringing response relay at the second switchboard responsive to the second connection of the source of alternating current with the trunk circuit, a local relay energized upon the response of both ringing relays for operating the signaling device, a' locking circuit in the local relay established upon the energization thereof, means responsive to the connection of the trunk circuit with the extension circuit for stopping the operation of the signaling device, and means rendered effective upon the subsequent response of the first ringing response relay for causing the operation of the signaling device.

5. A telephone exchange system comprising a trunk circuit extending from a first to ,a second switchboard, a link circuit at the first switchboard, a source of alternating current, a relay operating upon the connection of the link circuit with the trunk circuit, a second relay adapted when energized to connect the source of alternating current with the trunk circuit, an energizing circuit for the second relay established upon the operation of the first relay, a third relZLY'tllGlGflfttEI energized to open the energizing circuit of the second relay, a second energizing circuit for the second relay completed upon the disconnection of the link circuit from the trunk circuit while the third relay is energized, an extension circuit at the second switchboard, a signaling device thereat, and means responsive to the first connection or" the source of alternating current with the trunk circuit for operating the signaling device and again responsive to the second connection of the source of alternating current with the trunk circuit while connected with the extension circuit for again operating the signaling device.

6. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternat ing current, a relay energized upon the connection of the link circuit with the trunk circuit, a second relay adapted when operated to connect the source of alternating current with the trunk circuit, means cooperating in one manner with the first relay 'when energized to establish an o crating circuit for the second relay anEl cooperating in a different manner with the first relay when deenergized upon the disconnection of the link circuit from the trunk circuit to again establish an operating circuit for the second relay, an extension circuit at the second switchboard, a signaling device thereat, and means responsive to the first connection of the source of alternating current with the trunk circuit for operating the signaling device and responsive to the second connection of the source of alternating current with the trunk circuit while connected: with the extension circuit for again operating the signaling device.

7. A tele hone exchange system comprising a trun circuit extending from a first to a second switch-board, alink circuit at the first switchboard, a source of alternating current, a first relay energized upon the connection of the link circuit with the trunk circuit, a slow-release relay adapted when operatedto connect the source of alternating current with the trunk circuit, an opcrating circuit for the slow-release relay completed upon the energization of the first relay, a slow-operating relay responsive to the energization of the first relay, a second slow-iielease. relay energized upon the response of the slow-operating relay to open the operating circuit of the first slow-release relay, a second operating circuit for the first slow-release relay completed upon the deencrgization of the first relay when the link circuit is disconnected from the trunk circuit and including a contact of the energized sec ond slow-release relay, an extension circuit at the second switchboard, a signaling device thereat, and a relay at the second switchboard energized upon the first connection of the source of alternating current with the trunk circuit for operating the signaling device and deenergized upon the second connection of the source of alternating current with the trunk circuit while connected with the extension circuit for again operating the signaling device.

8. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, means in the trunk circuit responsive to the connection of the link circuit withthe trunk circuit for connecting thereto alternating current of one strength and responsive to the disconnection of the link circuit from the trunk circuit to connect therewith alternating current of another strength, an extension circuit at the second switchboard, a signaling device thereat, a ringing response relay at the second switchboard responsive to -the connection current of either strength with the trunk circuit, another ringing response relay at the second switchboard responsive to the connection of current of the higher strength with the trunk circuit, and a relay energized upon the response of both ringing response relays to operate the signaling device and denergized upon the subsequent response of the first ringing response relay while the trunk ci cuit is connected with the extension circuit for again operating the signaling deice.

9. Atelephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current, a relay for the trunk circuit momentarily responsive to the connection of the link .ci cuit with the trunk circuit for connecting therewith the source of alterhating current, a relay at the second switchboard responsive to the connect-ion of the source of alternating current with the trunk circuit, a si ,naling device operated upon the response of the second mentioned relay, an extension circuit at the second switchboard, means responsive to the connection of the trunk circuit with extension circuit to stop the operation of the signaling device, means effective upon the disconnection of the link circuit from the trunk circuit for causing the momentary response of the first mentioned relay to again connect the source of alternating current with the trunk circuit, and means at the second switchboard responsive to the second connection of the source of alternating current with the trunk circuit for causing the operation of the signaling device.

10. A telephone exchange system compris ing a trunk circuit extending from a first to a second switchboard, a signaling device at the first switchboard, a relay in the trunk circuit at the second switchboard, an extension circuit connected with the trunk circuit and extending from the second to a third switchboard, a telephone line termi nating at the third switchboard, means responsive to the connection of the extension circuit with the telephone line for operating the trunk relay, a source of alternating current, meansresponsive to the operation of the trunk relay for connecting the source of alternating current with the trunk circuit, a relay at the first switchboard responsive to the connection of the source of alter nating current with the trunk circuit for operating the signaling device, a source of ringing current at the first switchboard, means thereat for connecting the source of ringing current with the trunk circuit, ringlng response means in the trunk circuit responsive to the connection of v the ringing current therewith for causing the disconnection of the source of alternating current therefrom, a source of ringing current at the third switchboard, and a relay thereat operating upon the response of the ringing response means for connecting the source of ringing current thereat with the telephone line.

11. A. telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a signaling device at the first switchboard, a source of alternating current at the second switchboard, a relay thereat operating to connect the source of alternating current with the trunk circuit, a relay at the first switchboard responsive to the connection of the source of alternating current with the trunk circuit for operating the signaling device, a source of ringing current at the first switchboard, means thereat for connecting the source of ringing cur rent with the trunk circuit, ringing response means in the trunk circuit responsive to the connection of the source of ringing current therewith for causing the disconnection of the source of alternatincurrent therefrom, and a signal control re .ay energized upon. the response of the ringing response means.

19 A telephone exchange system comprising a trunk circuit extending from. a first to a second. switchboard, a signaling device at the first switchboard, .a source of alternating current at the second switch board, a relay thereat operating to connect the source of alternating current with the trunk circuit, a relay at the first switchboard responsive to the connection of the source ofalteinating current with the trunk circuit for operating the signaling device, a. source of ringing current at the first switchboard, means thereat for connecting the source of ringing current with the trunk circuit, a ringing response relay in the trunk circuit energized upon the connection of ringing current therewith to deenergize the first mentioned relay, thereby to disconnect the source of alternating current from the trunk circuit, and a signal control relay opcrating upon the energization of the ringing response relay;

13. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current, means in the trunk circuit responsive to the connection of the link circuit with the trunk circuit for connecting therewith the source of alternating current, a signaling device at the second. switchboard, means responsive to the connection of the source of alternating current with the trunk circuit to operate the signaling device, a-

source of ringing current at the first switchboard,.means to connect the source of ringing current with the trunk circuit, a relay in the trunk circuit responsive to the connection of the ringing current therewith for again causing the response of the first mentioned means, thereby to again connect the source of alternating current with the trunk circuit, and a signal control relay in the trunk circuit at the second switchboard responsive to the second connection of the source of alternating current therewith.

14. A telephone exchange system comprising a trunk circuit extending from a firs t to a second switchboard, a link circult at the first switchboard, a source of alternating current, a relay in the trunk circuit responsive to the connection of the link circuit with the trunk circuit for connecting therewith the source of alternating current, a signal.

ringing current at the first switchboard, a ringing key in the link circuit for connecting the source of ringing current with the trunk circuit, a ringing response relay energized upon the connection of the ringing current with the trunk circuit for again operating the first mentioned relay to connect the source of alternating current with the runk circuit, and a second signal control relay at the second switchboard responsive to the second connection of the source of alternating current with the trunk circuit.

15. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of current, a relay in. the trunk circuit adapted when energized to connect the source therewith, means rendered effective upon the connection of L the link circuit with the trunk circuit for causing the momentary energization of the relay, means cooperating with the first mentioned means upon the disconnection of the link circuit from the trunk circuit for causing the momentary energization of the relay, an extension circuit at the second switchboard, asignaling device thereat, and means responsive upon the first energization of the relay to operate the signaling device and 'difl'erently responsive upon the second energization of the relay while the trunk circuit is connected with the extension circuit for again operating the signaling device.

16. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a linkcircuit at the first switchboard, a relay in the trunkcircuit momentarily energized upon the connection of the link circuit with the trunk circuit and again momentarily energized upon the disconnection of the link circuit from the trunk circuit, a source of current connected with the trunk circuit while the relay is energized, an extension circuit at the second switchboard, a signaling device thereat, and means responsive upon the first energization of the relay to operate the signaling device and differently responsive upon the second energization of the relay while the trunk circuit is connected with the extension circuit for again operating the signaling .de-vi ce.

In witness whereof, we hereunto subscribe our names this 18th day of April A. D, 1918.

- WILLIAM R. BROUGH.

WILLIAM L. DODGE." 

